1. Field of the Invention
The present invention relates generally to a system for mounting equipment such as a transceiver antenna unit to a vehicle. More specifically, the present invention is directed to a system and apparatus for manual adjustment of the antenna unit and mast orientation relative to a moving boat to maintain a generally horizontal orientation of the equipment relative to an external frame of reference.
2. Description of the Background
Marine radar equipment has become increasingly easy and inexpensive to use and consequently is found on more and more small vessels including small sailboats. As is well known, marine radar systems detect objects such as other vessels or land masses at or near the surface of the water by transmitting radio waves or microwaves and detecting the return wave signal that is reflected by objects in their path. In order to provide information about objects in a wide area, radar systems typically use rotating antennas to sweep an arc in the horizontal plane H (FIG. 1A, 1B) partially or completely around the vessel while continually scanning for returned radio signals indicating the presence of an object. The range at which a radar system is capable of detecting the signal returned by an object is increased by elevating the antenna such that it is common to mount the antenna to the mast of a sailboat or to another point in the rigging above the deck in order to maximize operational range.
However, under sail a sailboat may be heeled over at an angle that can reach 45° or more in heavy winds, and 15° to 25° degrees under more common wind conditions. When a sailboat is heeled over the normally horizontal plane swept by a rotating antenna is likewise tipped or heeled to a similar angle, as depicted in FIG. 1B. On the leeward or downwind side of the boat the radar signal is directed downward toward the water's surface, where it is reflected or deflected resulting in false or distorted return signals. On the windward side the radar signal is directed upward, well above any objects of concern for the sailor resulting in no return signal at all. In either case the effective range and ability of the radar system to detect objects at or near the surface of the water in proximity to the vessel is severely compromised. The vertical beam width of the transmitted radar signal is typically 25° such that any heel angle over 12.5° will negatively impact radar performance.
Mounting devices for radar antennae have been provided previously for use on sailing vessels. Some mounting devices such as that described in U.S. Pat. No. 4,659,044 to Armstrong fix the position of the radar antenna and do not facilitate any pivotal movement to compensate for heeling. More recently, prior radar mounts such as that described in U.S. Pat. No. 5,154,386 have included a pivoting system which allows the mounted radar antenna to swing freely and assume a horizontal orientation under the force of gravity. Other prior art radar mounts such as is described in U.S. Pat. No. 6,097,344 to Anderson utilize an actuator system to actively level a radar antenna mount.
Each of these prior radar antenna mounting devices has drawbacks and limitations. For example, fixed radar antenna mounts allow radar systems to be used in only the calmest conditions with minimal heeling of the sailboat, as described above. Gravity oriented pivoting radar antenna mounting devices allow the radar antenna to swing freely and constantly as the vessel moves through the waves (and even at anchor) negatively impacting the accuracy of the radar system and excessively wearing the antenna connections and electrical cabling as well as the moving parts of the mount itself. Passive dampening elements may somewhat limit swinging but add complexity and expense to the system, require maintenance and are prone to wear and malfunction under marine conditions. Actively actuated (motorized) systems eliminate the wear associated with uncontrolled swinging but require power and control systems which are equally prone to wear and failure in a marine setting.
Typically, wind conditions remain fairly constant on a minute to minute basis and a sailboat tends to heel at a constant angle or range while sailing in a given direction. Thus, it is unnecessary to constantly adjust the radar antenna. It is sufficient, and much easier, to adjust the angle once at each tack, and therefore more practical to provide a manual adjustment feature, thereby reducing wear and tear of cabling.
It would be desirable to provide a system for elevated mounting of radar antenna on a sailing vessel that is capable of being quickly and easily leveled manually by an operator and yet which avoids the limitations, cost, complexity and power requirements of prior systems and which also avoids the continuous and debilitating wear induced by uncontrolled swinging of the mount.